Field of Endeavor
The present application relates to hydrogen and more particularly to hydrogen refueling with reduced hydrogen loss.
State of Technology
This section provides background information related to the present disclosure which is not necessarily prior art.
One of the main drawbacks of low temperature hydrogen storage systems is venting losses, which occur when the vessel pressurizes beyond its rated pressure due to heat transfer between the hydrogen and its surrounding environment. One way to limit that effect is building more efficient insulation devices. However, high performance insulation solutions add volume, mass, complexity and cost to the storage system; all of them needing to be reduced to propose a realistic cost effective commercial solution.
Alternatively, it can be shown that taking advantage of the unique properties of the hydrogen molecule could reduce venting losses using existing compact and cost-effective vessel designs. The hydrogen molecule has two different spin states: in one configuration, its spins are parallel (most energetic form, called ortho-H2) while in a second configuration they are anti-parallel (para-H2 form). Conversion from the low-energy para-H2 to the high-energy ortho-H2 is endothermic. As a result, the rate of pressure and temperature rise will diminish when this conversion is taking place, thus reducing venting losses. The para/ortho-H2 mixture is mainly a function of temperature and is likely to change at a rate that varies with heat transfer and density. Applicants have recently shown that the initial ortho-fraction plays a major role in promoting para/ortho-H2 kinetics. Initial ortho-fraction between 5 and 20% could increase dormancy (the time for which a cryogenic vessel can absorb heat from the surroundings without venting hydrogen vapor) by a factor 2 to 4 depending on temperature, density and volumes.